Closed-cell foam: rarely. Open-cell foam: occasionally for nesting material, not as a path. All penetrations are filled with closed-cell during install, which most pests find impassable. Crucial for attic installs.
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Closed-cell foam is dense (1.7-2.0 lb/cubic foot) and physically resistant to rodent gnawing. Mice rarely penetrate closed-cell unless an existing path provides easy access. Open-cell foam (0.4-0.8 lb/cubic foot) is softer and small rodents will tear out portions for nesting material in attics; this rarely creates a passage but can degrade thermal performance over years. Best practice in Cincinnati attic installs: spray closed-cell at all penetrations (chimney chase, plumbing stacks, electrical can lights, attic access trim) regardless of whether the rest of the attic uses open-cell or closed-cell. This blocks the most common rodent entry paths. Pre-install pest inspection: our Cincinnati installers note any active rodent activity during the on-site assessment; remediation precedes spray application if needed. Foam is not a substitute for proper exterior pest exclusion (sealing soffit gaps, repairing damaged vents); both work together. Cincinnati pre-install pest-inspection: our Cincinnati installers note any active rodent activity during the on-site assessment and recommend remediation before spray application if needed. Foam is not a substitute for proper exterior pest exclusion (sealing soffit gaps, repairing damaged vents, addressing crawl-space access points); both work together to eliminate ongoing pest issues.